4 research outputs found
Resistance to HER2-targeted therapies in HER2-positive breast cancer
Breast cancer accounts for 522,000 deaths worldwide each year and is the most common
cancer in women. It is classified according to the cell of origin and its expression of
several receptors: oestrogen and progesterone receptors, and human epidermal growth
factor receptor 2 (HER2).
Historically, HER2-positive breast cancers had a worse survival prognosis than oestrogen
or progesterone receptor-positive cancers, but the development of HER2-targeted
therapies led to significant survival improvements. Despite this, patients often present
with de novo resistance, or will develop acquired resistance to targeted therapies.
Several resistance mechanisms have been identified but attempts to target them have
failed. Thus, it is of paramount importance to identify the mechanisms used, to prevent
development of resistance or resensitise tumours to HER2-targeted therapies. Objectives
of this study were: to understand the link between epithelial to mesenchymal transition
(EMT) and loss of HER2, seen in a model of acquired resistance to the HER2-targeted
therapy, sapatinib, and to characterise and validate tumours from a sapatinib-treated
spontaneous mouse model of HER2-positive breast cancer.
The EMT-linked transcription factor ZEB1 was associated with acquired resistance to
sapatinib in tumours that had undergone EMT and concurrently lost HER2. Generation
of drug resistant cell lines failed to recapitulate the in vivo phenotype. Transient
overexpression of ZEB1 in vitro did not induce clear EMT or loss of HER2, despite
a trend towards lower HER2 expression. However, we found that treatment of cells
with ERBB2 shRNA, the gene encoding HER2, increased levels of ZEB1 and enhanced
migration, but did not induce overt EMT. This may be the result of differing PTEN
status between in vivo and in vitro models.
Treatment of a spontaneous mouse model of HER2-positive breast cancer with sapatinib
revealed that progressing tumours had an increase in proteins associated with cellular
iron homeostasis. Further investigation revealed increased heme oxygenase-1 (HO-1),
iron exporter ferroportin and altered iron storage.
To ascertain if modulation of dietary iron intake could affect the development of resistance
to sapatinib, mice were given a control or iron-deficient diet and treated with vehicle or
sapatinib. This showed that in sapatinib-treated mice fed an iron-deficient diet, HO-1
was not increased as in tumours from mice fed a iron-low control diet.
We looked at the possibility of HER2-targeting therapies inducing ferroptosis, an iron-dependent
form of cell death. Sapatinib-treated tumours from mice on a iron-low control
diet had increased cyclooxygenase 2 (COX2), a marker of ferroptosis, which was not
seen in sapatinib-treated tumours from mice on an iron-deficient diet. Additionally, in
vitro drug treatments with HER2-targeting agents showed that SKBR3 cell death could
be rescued by iron chelation.
HO-1 overexpression in SKBR3 cells revealed increased autophagic flux and resistance to
HER2-targeted therapies. Inhibition of autophagy reversed resistance, rendering them
susceptible to sapatinib- and lapatinib-induced cell death. Further, increased autophagic
flux was seen in all progressive tumours on sapatinib. The increased resistance to
sapatinib in mice fed an iron-deficient diet was also associated with increased autophagic
flux, although this was HO-1-independent.
Taken together, the results presented here provide a novel mechanism of cell death
induced by HER2-targeting agents in vitro and in vivo. We have shown that increased
HO-1 and reducing dietary iron can affect the development of resistance to sapatinib,
which is reliant on autophagy induction. Further, inhibiting autophagy can resensitise
cells to sapatinib and lapatinib treatment
A Distinct Macrophage Population Mediates Metastatic Breast Cancer Cell Extravasation, Establishment and Growth
Background: The stromal microenvironment and particularly the macrophage component of primary tumors influence their malignant potential. However, at the metastatic site the role of these cells and their mechanism of actions for establishment and growth of metastases remain largely unknown. Methodology/Principal Findings: Using animal models of breast cancer metastasis, we show that a population of host macrophages displaying a distinct phenotype is recruited to extravasating pulmonary metastatic cells regardless of species of origin. Ablation of this macrophage population through three independent means (genetic and chemical) showed that these macrophages are required for efficient metastatic seeding and growth. Importantly, even after metastatic growth is established, ablation of this macrophage population inhibited subsequent growth. Furthermore, imaging of intact lungs revealed that macrophages are required for efficient tumor cell extravasation. Conclusion/Significance: These data indicate a direct enhancement of metastatic growth by macrophages through their effects on tumor cell extravasation, survival and subsequent growth and identifies these cells as a new therapeutic target fo